A typical modular power supply system is designed to receive an AC electric power from a commercially available AC power source via power lines and deliver a DC electric power to one or more load devices through appropriate power regulation steps. A modular power supply system according to the prior art is illustrated in FIG. 1. The modular power supply system 10 of FIG. 1 substantially includes an AC power source 11, an EMI filter 12, a bridge rectifier 13, and a DC—DC converter 14. The AC power source 11 is used to accommodate an input AC voltage, while the EMI filter 12 is used to suppress the electromagnetic interference components persisting in the input AC voltage. The bridge rectifier 13 is connected to the EMI filter 13 for converting the filtered AC voltage into a desired input voltage, and the DC—DC converter 14 is configured to receive the rectified input voltage from the full-wave bridge rectifier 13 and convert the input voltage into a desired output DC voltage tailored to power a load device (not shown).
Moreover, the modular power supply system 10 further includes a power status signal generator circuit 15 that can monitor the power supply status of the AC power source 11 and detect the voltage sag problem of an input peak voltage of the AC power source 11 in the event that the AC power source 11 is malfunctioned or was removed from the modular power supply system 10. The power status signal generator circuit 15 according to the prior art generally includes a half-wave rectifier 151, a RC charging/discharging network 152, a RC filter 153, and a voltage comparator 154. The AC voltage supplied by the AC power source 11 is first rectified by a half-wave rectifier 151, which is generally implemented as a diode element. Next, a RC charging/discharging network 152, constituted by a capacitor C100 and a resistor R100, is used to perform charging/discharging operation to the capacitor C100 in order to detect the peak value of the input AC voltage in terms of the voltage across the capacitor C100. A RC filter 153, connected to the RC charging/discharging network 152, acts as a second-order low pass filter to filter and smooth the voltage across the charging/discharging capacitor C100. The output of the RC filter 153 is transmitted to an inverting input terminal of the voltage comparator 154 and compared with a reference voltage Vref, so as to determine whether the peak value of the input AC voltage from the AC power source 11 has dropped below a predetermined level. If the peak value of the AC voltage is dropped below a predetermined level, the voltage comparator 154 outputs a power status signal (AC-OK signal or AC-BROWNOUT signal) indicating the AC power source 11 is working normally or the AC power source 11 is deteriorating.
As described herein, the main function of the power status signal generator circuit 15 of FIG. 1 is to detect the peak value of the input AC voltage and determine whether the peak value of the input AC voltage has dropped below a predetermined level. In a typical modular power supply system, the frequency of an input AC voltage is rated at 50 Hz, that is, the period between two adjacent peaks of the input AC voltage should be rated at 20 microseconds. If the peak value of the input AC voltage is suddenly dropped below a predetermined nominal value, it may cause the whole system to halt its operation or lead the whole system to faulty operation. In order to detect the voltage sag problem of the input AC peak voltage as quickly as possible, the power status signal generator circuit 15 is required to detect the voltage sag problem of the input AC peak voltage and send an appropriate power status signal to inform the system of the AC failure condition in response to the voltage sag detection within a short period, so that the diagnosis function of the modular power supply system can be activated to discriminate the actual cause of the defective system operation.
A common requirement of the period set to detect the voltage sag problem of an input AC peak voltage is stipulated to be a power supply cycle of the input AC voltage, that is, 20 microseconds. However, the prior art power status signal generator circuit 15 suffers from several major drawbacks so that it is unable to meet such requirement. One of the major problems stems from the RC filter 153. In order to derive a smoother voltage waveform curve, the capacitor used in the RC filter 153 is generally implemented with a bulk capacitor. In this way, a significant time delay amount introduced by the RC filter 153 will be imposed on the period set to detect the voltage sag problem. That is to say, in the event of AC failure condition, the power status signal generator circuit 15 can not determine the voltage sag problem of the input AC peak voltage and send an appropriate power status signal to the modular power supply system 10 at the instant the defective system operation occurs, but will be delayed for a considerably long time. In practical operation, this time delay amount is measured up to 100 microseconds. Under this condition, the modular power supply system 10 can not identify the actual cause of the defective system operation immediately. Such a measurable time delay amount is sometimes intolerable, and can not comply with the requirement of fast sag detection of the input AC peak voltage caused by the AC power source 11.
In view thereof, there is a tendency to develop a modular power supply system that includes a power status signal generator circuit capable of performing a fast sag detection of an input AC peak voltage. The present invention can satisfy these needs.